Advanced analysis of hybrid steel and concrete frames: Part 1: Cross-section analysis technique and second-order analysis

Abstract

Hybrid frames composed of steel, concrete and composite members are widely used to-date due to their structural efficiency and economy as alternatives to traditional bare steel system, especially in high-rise buildings. However, the present design of this structural form is both inconvenient and inconsistent as it needs several separated design codes for bare steel (BS), reinforced concrete (RC) and steel-concrete composite (SCC) elements. This paper proposes a second-order design method which requires only section capacity check without the need of using prescriptive formulae in different codes for various structural forms. The member-based design using linear analysis and the effective length assumption is replaced by the iterative second-order analysis. Using the Pointwise-Equilibrium-Polynomial (PEP) element, which allows for member P-δ effects and initial imperfections in conjunction with a robust nonlinear incremental-iterative procedure, the nonlinear response of individual members and the structural system is captured directly and used for structure resistance checks. The sectional failure surface method is introduced for member strength checking. In the generation of failure surfaces of the arbitrarily shaped cross sections, the stress distribution along the concrete component is considered by an equivalent stress block or a number of segments and the entire structural steel section will be meshed into fibres for determination of section capacity. Verifications of the proposed integrated analysis and design method based on section capacity check are conducted using several examples with accuracy of the method demonstrated.